Many diseases arise from the growth and spread of microorganisms that can affect all aspects of life, from human health, to animal health, to food and water safety, to the safety of the environments we live in. Oxidizers and disinfectants have found wide spread application in all these areas. Hospitals perform rigorous programs to disinfect and sterilize their environments. Consumer homes are replete with disinfectant hand cleaners, sprays, hard surface cleaners, disinfectant wipes, and fruit and vegetable washes. Disinfectants are widely used on farms where the difference between healthy and sick animals can mean the difference between profitability and loss.
Acidified chlorite (AC) oxidizers are commonly formed from two-part products having a first or base part containing a chlorite (such as sodium chlorite) and a second or activated part containing an acid activator. The AC oxidizer is formed upon mixing the first and second parts, and typically only in amounts sufficient for a given use period. Depending on the desired characteristics and/or intended use of the AC oxidizer, either the first or second part, or both parts, may contain one or more additional functional ingredients. Also, depending on the two-part system, the AC oxidizing composition may be formed by simply mixing the first and second parts, often in approximately equal volumes, or may involve some additional dilution step before or after mixing.
Acidified chlorite compositions may be generated by combining a source of chlorite ions (i.e., ClO2−), typically in the form of a metal salt such as sodium chlorite, with an acid activator. Such compositions are effective oxidizers due to the generation of antimicrobial oxidants, particularly chlorous acid (i.e., HClO2). Chlorous acid is formed very rapidly upon acidification of chlorite in an equilibrium process governed by the solution pH.
AC compositions differ significantly from compositions that are designed to produce chlorine dioxide. Chlorine dioxide compositions contain high amounts of chlorite and acid which is typically a mineral acid such as hydrochloric acid. The lower the pH of the composition, the faster the formation of chlorine dioxide. These reactions are described in detail in U.S. Pat. Nos. Re 36,064 and 6,063,425 which are incorporated by reference herein in their entirety.
Previously, a preferred acid activator for AC compositions has been an organic acid and preferably citric acid because the pH of organic acids is typically higher than the pH of mineral acids therefore allowing for the controlled formation of chlorous acid without the chlorous acid rapidly degrading to chlorine dioxide. In addition, citric acid is a food additive or GRAS (generally recognized as safe) acid meaning that it can be applied directly to food and food contact surfaces without being rinsed off. However, organic acids, and citric acid in particular, have several undesirable side effects.
AC compositions are used as an antimicrobial on food products and in particular poultry products. Spent water in poultry plants has to be treated to remove impurities from the water before being reused or being sent outside the plant. Fats and oils from poultry are some of the components of plant wastewater that need to be removed. One method of removing fats and oils from plant wastewater is using dissolved air floatation (DAF) which floats the fats and oils in solution to the top of the water where they can be skimmed off the surface and either disposed of or used. Fats and oils typically have charges associated with them which make them repel other fat and oil particles, negatively impacting coagulation and/or coalescing. When using DAF a coagulant may be used to neutralize charges on the fats and oils and make them more likely to form larger globules that are more likely to float to the top. Typical coagulants include metal salts such as FeCl2, FeCl3, FeSO4, or Al2(SO4)3. In addition to using a coagulant, a flocculant may also be used after the coagulation step. Flocculants are typically polymers that are designed to bridge fat and oil particles in solution together to form larger particles that are more likely to float to the top. Most of the wastewater treatment costs in food processing facilities are associated with adding coagulants and flocculants to the water.
Citric acid is a sequestrant and interferes with the ability of the coagulant to work effectively because the cations of the coagulant (that is the metal ions) are tied up to the citric acid and is no longer free to neutralize the surface charges of the fats and oils in the water. This has many negative side effects. More coagulant must be added to neutralize the fats and oils which increases the operation costs of a plant. The combination of citric acid and coagulant forms a solid which must be removed from the water and disposed of. The process quality goes down and the manpower needed to make the process work increases which means increased costs for the plant. More flocculant must be added which also increases the operation costs for the plant.
The solids may be disposed of in several ways. For example, the solids may be disposed of by collecting them and applying them to the land. However, approval from local authorities must be obtained first. The solids may be incorporated into feed or feed additives for animals. However, sometimes the solids contain too many metal cations to be used as a feed additive. Finally, the solids may be placed in a landfill. However, depositing material in landfills is environmentally undesirable and not all states allow this practice.
In addition to increasing the solids, citric acid usage increases the turbidity of the wastewater. High turbidity or high solids in the wastewater is undesirable because it creates places for bacteria to grow in the water. Further high turbidity increases the COD or chemical oxygen demand of the wastewater which is undesirable. COD is a measure of the level of organics in the water. The higher the COD, the more organics are present in the water. Organics are undesirable because they provide a food for bacteria to grow. Further, wastewater discharge rules limit the quantity of organics that can be in the effluent wastewater. Finally, high turbidity or high solids in water is aesthetically undesirable.
Another undesirable side effect of citric acid on wastewater treatment is the diminished removal of phosphorous from the wastewater. Plants use phosphorous compounds (generally in the form of phosphates) in several places including cleaning solutions, and meat tenderizers/stabilizers in poultry plants. Phosphorous must be removed in wastewater treatment before being released into the environment because phosphorous contributes to the eutrification, or algae growth, in wastewater or the body of water that the wastewater is released into. Consequently, the phosphorous must be removed or the plant has to pay to have it be removed or is fined if the phosphorous level is not low enough. During the wastewater treatment process, the phosphorous is precipitated out of solution and can then be removed. However the citric acid causes the phosphorous to remain in solution in the wastewater, which makes it more difficult to remove during the wastewater treatment process.
After the water is treated using DAF, the water goes to biological treatment to remove organics from the water. The wastewater treatment plant may be either a publicly owned treatment works (POTW) facility or part of the food processing plant facility. Biological treatment uses aerobic and anaerobic bacteria to remove organics from the water prior to discharge into a receiving stream. Regulatory agencies look at the health of certain sensitive organisms including Daphnia and fat-head minnows in the receiving stream as an indication of the quality of the water treatment process. Because Daphnia are sensitive to the ionic strength of the water, controlling the number of ions in the water is important to keeping them healthy. Citric acid based acidified sodium chlorite compositions add a significant amount of ions to the water in a typical poultry plant (˜10,000 to 14,000 ppm ions), most of which come from the citric acid. This process constitutes 1-2% of the total wastewater discharge of a typical poultry slaughter facility. With this dilution, the resulting contribution of 100 to 280 ppm of ions may negatively impact the health of the biota in the receiving streams.
In recent years, high energy costs, high water costs, high wastewater disposal costs, high solid waste disposal costs, and high raw material costs have become a reality for plant operators. Additionally, awareness continues to increase on protecting the environment by recycling instead of depositing materials in landfills, using less water, using less energy, protecting resources, and generally negatively impacting the environment as little as possible. Compositions and processes like AC compositions using citric acid require more energy and raw materials to work effectively and to remove impurities and pollutants from the wastewater, and they generate more solid byproducts that need to be disposed of. A need exists for more environmentally friendly, or “green” AC compositions that work just as well antimicrobially as organic acid based AC compositions, but without the negative environmental side effects.
In addition to negative side effects on wastewater treatment, the use of organic acids, and citric acid in particular, have several other undesirable characteristics. For example, because citric acid is a sequestrant the citric acid negatively reacts with water hardness ions such as calcium and magnesium if the plant is using hard water. The result is that significantly more citric acid must be used in order to generate a sufficient amount of chlorous acid which increases costs for the plant. Also, citric acid has been observed to discolor chicken wings which creates an undesirable product for the consumer. Further, the pH of citric acid levels out between pH 2 to 3 in that if more citric acid is added, the pH does not change significantly. This is due in part to the buffering capabilities of citric acid. If a lower pH is desired, a significant amount of citric acid must be added in order to lower the pH below its buffering range. Finally, because citric acid is an organic acid, it can potentially leave behind carbon residues that bacteria can grow on which is undesirable.
It is against this background that the present invention has been made.